PBT resins are semicrystalline thermoplastics used in a variety of durable goods. PBT resins are now widely used for components in the electronics and automotive industries. As these market sectors continue to expand and evolve, demand for PBT has continued to grow. Thus, in 2009, worldwide consumption of PBT was reported to total 750 kilotons. Demand for PBT is projected to increase at least 5 percent per year, leading to a projected demand of 1300 kilotons by the year 2020.
PBT producers continue to face the challenge of meeting increasing demand for PBT while dealing with higher production costs. One approach to improving process yield and reducing cost on an industrial scale relates to using PBT oligomer to make PBT resins. PBT oligomer can be prepared from PTA and BDO. To be useful in making PBT resin for specific end purposes, it is necessary to strictly control the carboxylic acid end group concentration [CEG] and IV values of the PBT oligomer. PBT oligomers consisting of high carboxylic acid end group concentration (greater than 100 mmol/kg) are valuable for thermoset and composite applications due to the high carboxylic acid functionality. These oligomers are also important intermediates for making PBT via either a continuous or batch processes. Undesirable side reactions such as backbiting and thermal degradation limit the quality of the PBT oligomers for further processing. When thermal degradation and backbiting occur, the molecular weight increase of PBT is reduced.
As a result, there remains a need for new and improved processes for making PBT resins from PBT oligomer with desired IV and [CEG] values and minimized rates of degradation side reactions.